This invention relates to a method and apparatus for counterflow heat exchange between solids in which the solids are brought into contact with one another to facilitate the heat exchange.
A common and recurring industrial need is that of transferring heat to or removing heat from materials for the purpose of, for example, preparing such materials for processing operations which are to be carried out at certain temperatures. After the processing, it is oftentimes desirable to bring the temperature of the material back to its previous temperature for storage, packaging, etc.
Heat transfer or exchange between fluids is oftentimes accomplished by the well known process of placing two fluids of differing temperature in as close proximity as possible with each other. One of the simplest ways of doing this is to place a small pipe inside a larger pipe and then apply one fluid to the small pipe and the other fluid to the larger pipe (outside the smaller pipe). If the two fluids are applied to the pipe so that they both flow in the same direction (parallel flow), then the temperatures of the two fluids tend toward the average therebetween. If the fluids are applied to the pipes to flow in opposite directions (counterflow), then the temperature of each fluid tends toward the other fluid's entering temperature.
There have been a number of suggestions for providing a heat exchange between solid materials including those disclosed in U.S. Pat. Nos. 2,592,783 and 4,038,021 and in copending patent application, Ser. No. 943,057. In the first mentioned patent, heated or cooled balls are brought into direct contact with a material to be either heated or cooled inside a rotating drum. The balls are piled up in one end of the rotating drum and the material in the other end and the rotation of the drum tends to move the balls and material towards one another in a type of counterflow operation to somehow mix so that heat can be exchanged between the balls and the material.
The structure disclosed in the second mentioned patent includes an inclined tubular casing and an auger disposed within the casing, with the flights of the auger being perforated. A granular product to be dried and heat conducting particles such as salt, are discharged into the casing from an opening in the bottom end of a tubular shaft of the auger. As the auger is rotated, the granular product and heat conducting particles are in some manner intermixed, with the granular product being forced upwardly in the casing since the product is of a size too large to pass through the holes in the auger flights, and the heat conducting particles apparently staying near the bottom of the casing since the particles are small enough to pass through the holes in the auger flights. This arrangement, of course, does not provide for a counterflow operation but rather provides for a type of mixing of two different size particles and then the removal of one size from the mixture.
In the above-mentioned patent application, a countercurrent heat transfer device is shown to include an inclined, rotatable, cylindrical drum in which is disposed a helical auger whose outer lip is maintained in contact with the interior wall of the drum. The auger includes a plurality of openings so that when a fine material is introduced into the upper end of the drum and a coarse material is introduced into the lower end of the drum, and the drum is rotated, the fine material sifts through the auger and the coarse material is carried by the auger to the upper end of the drum. In this manner, the coarse and fine material contact one another to exchange heat.